The present invention relates to microcellular foams, and more particularly to the use of microcellular foams for uses such as transducer diaphragms.
Microcellular foams are made by supersaturating a polymeric material with a gas, heating the polymeric material to near its glass transition temperature, then cooling the material. This process causes the nucleation of small gas-filled voids, called cells, in the polymeric material, thereby causing the material to expand. Cooling the material causes expansion in the nucleation to stop. A method for manufacturing microcellular foam is described in U.S. Pat. No. 4,473,665 issued Sep. 25, 1984, to Martini-Vvedensky et al. Microcellular foams made by conventional processes have cell sized in the range of 2 to 25 microns.
Another class of microcellular foam is called supermicrocellular foam, which is made by supersaturating a polymeric material with a fluid in a supercritical state. Conventional supermicrocellular foam has cell sizes in the range of 0.1 to 2.0 microns. A method for manufacturing supermicrocellular foams is described in U.S. Pat. No. 5,158,986, issued Oct. 27, 1992 to Cha et al
It is an important object of the invention to provide improved microcellular foams, transducer diaphragms and methods of making them.
According to the invention, a method for producing a foamed polymeric material includes saturating a portion of unfoamed material with a fluid; and causing the material to expand in thickness while remaining substantially unexpanded in its other dimensions.
An aspect of the invention, a method for forming a foamed polymeric object, includes the steps of preforming or shaping the object from an unfoamed polymeric material having a planar crystalline structure; saturating the object with a fluid; and reducing the ambient pressure to a pressure at which the material is supersaturated with the fluid.
In another aspect of the invention, a foamed polymeric material has gas filled cells each having one dimension that is larger than a second dimension.
In yet another aspect of the invention, a foamed polymeric material with gas filled voids having a first dimension of less than 30 microns measured in the direction of the thickness of the material forms a transducer diaphragm.